Distinguish between peer-to-peer and client-server networks
Identify types of applications and protocols used on a network
Describe various networking hardware devices
able to draw network diagrams
1-1 History of Comms
History of Communication
Speed, distance, and cost are the drivers of communications
technology
Approaches to long-distance communications
Couriers
Telegraphy
Computer networks
History of Communication
Couriers physically transport messages
messenger pigeons, pony express, AusPost
Can overcome great distances, but are slow and costly
History of Communication
Telegraphs transmit messages using signals
drums, beacons, mirrors, smoke, flags, what else (can you think
of any)?
Optical telegraphs were invented inthe 1790s and could propagate
signals 800km in 3 minutes
Optical telegraphs were replaced byelectric telegraph networks
Faster and cheaper
History of Communication
Electric telegraphs, and early telephone systems, still required a lot
of human intervention
Coding and decoding messages
Manually switching circuits
Messages are encoded,switched, and routedautomatically in
computernetworks
Therefore faster and cheaper
1-2 Network Models
Network Models
Topology describes how parts of a whole work together
Physical topology mostly refers to a network’s hardware and how
computers, other devices, and cables work together to form the
physical network
Logical topology refers to how software controls access to network
resources
includes how users and software initially gain access to the
network
network operating system (NOS) controls access to the entire network
NOS is required by client-server models
Peer-to-Peer Network Model (1 of 2)
a peer-to-peer (P2P) network model the OS of each computer on the
network is responsible for controlling access to its resources
There is no centralised control
Computers, called nodes or hosts, form a logical group of computers
and users
Each computer controls its own administration, resources, and
security
Advantages
Simple configuration
Less expensive compared to other network models
Disadvantages
Not scalable
Not necessarily secure
Not practical for large installations
Peer-to-Peer Network Model (2 of 2)
Figure 1-1 In a peer-to-peer network, no computer has
more authority than another; each computer controls its
own resources and communicates directly with other
computers
Client-Server Network Model (1 of 3)
Resources are managed by the NOS via a centralised directory
database
Windows domain is a logical group of computers that a Windows Server
can control
Client-Server Network Model (1 of 3)
Active Directory (AD) is the centralised directory database that
contains user account information and security for the entire group
of computers
user can sign on to the network from any computer on the network and
gain access to the resources that AD allows
This process is managed by Active Directory Domain Services (AD
DS)
computer making a request from another is called the client
Client-Server Network Model (2 of 3)
Figure 1-2 A Windows domain uses the client-server model to
control access to the network, where security on each computer or
device is controlled by a centralised database on a domain
controller
Client-Server Network Model (3 of 3)
The NOS is responsible for:
Managing client data and other resources
Ensuring authorised user access
Controlling user file access
Restricting user network access
Dictating computer communication rules
Supplying applications and data files to clients
Servers that have a NOS installed require:
More memory, processing power, and storage capacity
Equipped with special hardware to provide network management
functions
Client-Server Applications (1 of 2)
Network services are the resources a network makes available to its
users
includes applications and the data provided by these
applications
client-server applications:
client computer requests data or a service from a second
computer, called the server
Client-Server Applications (2 of 2)
Figure 1-3 A web browser (client application) requests a web page
from a web server (server application); the web server returns the
requested data to the client
Network Services and Their Protocols (1 of 2)
Protocols are methods and rules for communication between networked
devices
Two primary network protocols:
TCP (Transmission Control Protocol)
(Internet Protocol)
Popular client-server applications include:
Web service
Email services
DNS service
FTP service
Database services
Remote access service
Network Services and Their Protocols (2 of 2)
Figure 1-5 SMTP is used to send email to a recipient’s email server,
and POP3 or IMAP4 is used by the client to receive email
1-3 Network Models
Network Hardware
Figure 1-7 This LAN has five computers, a network printer, a local
printer, a scanner, and a switch, and uses a star topology
LANs and Their Hardware (1 of 4)
LAN (local area network) is usually contained in a small space
switch receives incoming data from one of its ports and redirects it
to another port or multiple ports
Will send the data to its intended destination
The physical topology used by this network is called a star topology
All devices connect to one central device (usually a switch)
NIC (network interface card) is a network port used to attach a
device to a network
Also called a network adapter
LAN can have several switches
backbone is a central conduit that connects the segments (pieces) of
a network
LANs and Their Hardware (2 of 4)
Figure 1-11 This local network has three switches and is using a
hybrid topology
LANs and Their Hardware (3 of 4)
router is a device that manages traffic between two or more networks
Can help find the best path for traffic to get from one network
to another
Routers can be used in small home networks to connect the home LAN
to the Internet
Called a SOHO (small office-home office) network
Industrial-grade routers can have several network ports, one for
each network it connects to
Difference between router and switch:
router is like a gateway between networks and belongs to two or
more local networks
switch belongs only to its local network
LANs and Their Hardware (4 of 4)
Figure 1-14 (a) A router stands between the LAN and the Internet,
connecting the two networks; (b) Home networks often use a combo
device that works as both a switch and a router
MANs and WANs (1 of 2)
WAN (wide area network) is a group of LANs that spread over a wide
geographical area
MAN (metropolitan area network) is a group of connected LANs in the
same geographical area
Also known as a campus area network (CAN)
MANs and WANs often use different transmission methods and media
than LANs
PAN (personal area network) is a much smaller network of personal
devices
network of personal devices such as your smartphone and your
computer
Other network types:
BAN (body area network)
SAN (storage area network)
WLAN (wireless local area network)
MANs and WANs (2 of 2)
Figure 1-17 A WAN connects two LANS in different geographical areas
Network Diagrams
Network Diagrams (1 of 6)
Network diagrams are graphical representations of a network’s
devices and connections
They may show physical layout, logical topology, IP address
reserves, names of major network devices, and types of
transmission media
Network mapping - the process of discovering and identifying the
devices on a network
Nmap – one of the most popular tools used for network mapping
Zenmap – Nmap’s GUI option
Cisco Systems set the standard for diagram symbols used to represent
network devices
Network Diagrams (2 of 6)
Network Diagrams (3 of 6)
Network Diagrams (4 of 6)
Network diagrams provide broad snapshots of a network’s physical or
logical topology
Useful for planning where to insert a new switch or determining
how a particular router, gateway, or firewall interact
Wiring schematic is a graphical representation of a network’s wired
infrastructure
detailed form, it shows every wire necessary to interconnect
network devices
Rack diagram is a drawing that show devices stacked in a rack system
Network Diagrams (5 of 6)
Network Diagrams (6 of 6)
Labelling and Naming Conventions (1 of 3)
Tips for labelling and naming conventions:
Use names that are as descriptive as possible
Only include fields that are essential in identifying the device
Don’t overcomplicate the name with useless or redundant
information
Use established naming conventions
Think big-picture-down-to-details
Labelling and Naming Conventions (1 of 3)
Tips for labelling and naming conventions:
Consider any security risks from details included in your naming
convention
Use colour-coded cables and use cable tags to identify each
cable’s purpose
Label the ports and jacks that cables connect to
Where labels won’t fit on the device, draw a simple diagram of
each device that indicates how each port is used
Use labels that are durable and are designed to stick to plastic
and metal
Labeling and Naming Conventions (2 of 3)
Labelling and Naming Conventions (3 of 3)
Week 2 Overview
Topics
OSI reference model
Physical transmission
Safety and troubleshooting network
Learning Objectives
Describe the seven layers of the OSI model
Explain best practices for safety when working with networks and
computers
Describe the seven-step troubleshooting model for troubleshooting
network problems
Explain basic data transmission concepts, including frequency,
bandwidth, throughput, multiplexing, and common transmission flaws
Explain best practices for safety when working with networks and
computers
2-1 OSI
The Open Systems Interconnection Model (OSI Model)
The Seven-Layer OSI Model (1 of 2)
The Seven-Layer OSI Model (2 of 2)
Layer 7: Application Layer
The application layer describes the interface between two
applications, on separate computers
Application layer protocols are used by programs that fall into two
categories:
Provide services to a user, such as a browser and Web server
Utility programs that provide services to the system, such as
SNMP (Simple Network Management Protocol) programs that monitor
and gather information about network traffic
Payload is the data that is passed between applications or utility
programs and the OS
Layer 6: Presentation Layer
The presentation layer is responsible for reformatting, compressing,
and/or encrypting data in a way that the receiving application can
read
Example:
email message can be encrypted at the Presentation layer by the
email client or by the OS
Layer 5: Session Layer
The session layer describes how data between applications is synched
and recovered if messages don’t arrive intact at the receiving
application
The application, presentation, and session layers are intertwined
often difficult to distinguish between them
Most tasks are performed by the OS when an application makes an API
call to the OS
API (application programming interface) call is the method an
application uses when it makes a request of the OS
Layer 4: Transport Layer
The transport layer is responsible for transporting Application
layer payloads from one application to another
Two main Transport layer protocols are:
TCP (Transmission Control Protocol) - makes a connection with
the end host, checks whether data was received; called a
connection-oriented protocol
UDP (User Datagram Protocol) - does not guarantee delivery by
first connecting and checking whether data is received; called a
connectionless protocol
Layer 4: Transport Layer
Protocols add control information in an area at the beginning of the
payload (called header)
Encapsulation is the process of adding a header to the data
inherited from the layer above
The Transport layer header addresses the receiving application by a
number called a port
a message is too large, TCP divides it into smaller messages called
segments
UDP, the message is called a datagram
Layer 3: Network Layer
The network layer is responsible for moving messages from one node
to another until they reach the destination host
The principal protocol used by this layer is IP (Internet Protocol)
adds its own network layer header to the segment or datagram
The entire network layer message is called a packet
Layer 3: Network Layer
IP address is an address assigned to each node on a network
The network layer uses it to uniquely identify each host
relies on several routing protocols to find the best route for a
packet to take to reach destination
ICMP and ARP are examples
Network layer protocol will divide large packets into smaller
packets in a process called fragmentation
Layer 2: Data Link Layer
Layers 2 and 1 are responsible for interfacing with physical
hardware on the local network
Protocols at these layers are programmed into firmware of a
computer’s NIC and other hardware
Type of networking hardware or technology used on a network
determine the data link layer protocol used
Ethernet and Wi-Fi are examples
Layer 2: Data Link Layer
The data link layer puts control information in a data link layer
header and at the end of the packet in a trailer
The entire data link layer message is called a frame
MAC (Media Access Control) address is also called a physical
address, hardware address, or data link layer address
embedded on every network adapter
Layer 1: Physical Layer
The physical layer is responsible for sending bits via a wired or
wireless transmission
Bits can be transmitted as:
Wavelengths in the air
Voltage on a copper wire
Light (via fibre-optic cabling)
Protocol Data Unit or PDU
Protocol data unit (PDU) is the technical name for a group of bits
as it moves from one layer to the next and from one LAN to the next
Technicians loosely call this group of bits a message or a
transmission
Summary of How the Layers Work Together
2-2 Physical Transmission
Physical Transmission
Transmission Basics
Transmission techniques in use on today’s network are complex and
varied
This section covers:
Measurements that indicate network efficiency
Obstacles to good network performance
Frequency, Bandwidth, and Throughput
Frequency is typically measured in MHz or GHz, which indicates the
number of times in a second that an electrical signal can change
states
Bandwidth is the amount of data that could be theoretically
transmitted during a given period of time
Throughput is the measure of how much data is actually transmitted
during given time period
New technologies such as modulation (sending data over an analogue
signal) and encoding (converting data into a digital signal for
transmission) offer methods for increasing theoretical bandwidth and
effective data throughput given the same maximum frequency
Transmission Flaws (1 of 2)
Noise is any undesirable influence degrading or distorting signal
Noise is measured in dB (decibels)
Two common sources of noise include the following:
EMI (electromagnetic interference) is caused by motors, power
lines, televisions, copiers, fluorescent lights, etc…
One type of EMI is RFI (radio frequency interference)
Cross-talk occurs when the signal on one wire infringes on
adjacent wire signal
Alien cross-talk occurs between two cables
Near end cross-talk (NEXT) occurs near source
Far end cross-talk (FEXT) occurs at the far end
Transmission Flaws (2 of 2)
Attenuation is the loss of a signal’s strength as it travels away
from source
Signals can be boosted using a repeater, which regenerates a digital
signal in its original form without noise previously accumulated
Latency is the delay between signal transmission and receipt
Latency may cause network transmission errors
The length of the cable affects latency, as does the existence of
any intervening device
Transmission Flaws (2 of 2)
RTT (round trip time) is the time for packet to go from sender to
receiver, then back from receiver to sender
packets experience varying amounts of delay they can arrive out of
order
problem commonly called jitter or PDV (packet delay variation)
Duplex, Half-Duplex, and Simplex (1 of 2)
NIC settings include the direction in which signals travel over the
media and the number of signals that can traverse the media at any
given time
These two settings are combined to create different methods of
communication
Full-duplex – Signals travel in both directions over a medium
simultaneously
Half-duplex – Signals may travel in both directions but only in one
direction at a time
Simplex – Signals may travel in only one direction and is sometimes
called one-way or unidirectional, communication
Windows, use Device Manager to configure a NIC, including speed and
duplex settings
Duplex, Half-Duplex, and Simplex (2 of 2)
Multiplexing (1 of 2)
Multiplexing is a form of transmission that allows multiple signals
to travel simultaneously over one medium
carry multiple signals, the medium’s channel is logically separated
into multiple smaller channels, or subchannels
Multiplexer (mux) is a device that combines many channel signals
required at the transmitting end of the channel
Multiplexing (1 of 2)
demultiplexer (demux) separates the combined signals on the
receiving end
Three types of multiplexing are used on copper lines:
TDM (Time division multiplexing) divides a channel into multiple
time intervals
STDM (statistical time division multiplexing) assigns slots to
nodes according to priority and need
FDM (Frequency Division Multiplexing) assigns different
frequency band for each communications subchannel
Multiplexing (2 of 2)
Three types of multiplexing are used on fiber-optic cable
WDM (Wavelength Division Multiplexing) carries multiple light
signals simultaneously by dividing a light beam into different
wavelengths or colors
DWDM (Dense Wavelength Division Multiplexing) increases the
number of channels provided by normal WDM
CWDM (Coarse Wavelength Division Multiplexing) lowers cost by
spacing frequency bands wider apart to allow for cheaper
transceiver equipment
2-3 Safety and Troubleshooting Network
Safety and Troubleshooting Network Problems
Safety Procedures and Policies
Network and computer technicians need to know how to protect
themselves
wells as protect sensitive electronic components
This section takes a look at some best practices for safety
Emergency Procedures
Know the best escape route or emergency exit
Fire Suppression Systems - have a fire suppression system in the
data center that includes:
Emergency alert system
Portable fire extinguishers
Emergency power-off switch
Emergency Procedures
Ask yourself: Does the security system allow access during a failure
(fail open) or deny access during the failure (fail close)?
SDS (safety data sheet) explains how to properly handle substances
such as chemical solvents and how to dispose of them
Includes information such as identification, first-aid measures,
fire-fighting measures, accidental release measures, handling
and storage guidelines, exposure controls, and physical and
chemical properties
Safety Procedures (1 of 4)
Electrical and tool safety is generally regulated by OSHA
(Occupational Safety and Health Administration)
OSHA guidelines when using power tools:
Wear PPE (personal protective equipment)
Keep all tools in good condition and properly store tools not in
use
Use the right tool for the job and operate the tool according to
the manufacturer’s instructions
Watch out for trip hazards, so you and others don’t stumble on a
tool or cord
Safety Procedures (2 of 4)
Lifting Heavy Objects - follow these guidelines:
Decide which side of object to face so load is most balanced
Stand close to the object with your feet apart
Keep your back straight, bend knees and grip load
Lift with your legs, arms, and shoulders (not your back or
stomach)
Keep the load close to your body and avoid twisting your body
while you’re holding it
put the object down, keep your back as straight as possible and
lower object by bending your knees
Safety Procedures (3 of 4)
Protecting Against Static Electricity
Computer components are grounded inside a computer case
Grounding means that a device is connected directly to the earth
Sensitive electronic components can be damaged by ESD (electrostatic
discharge)
Static electricity can cause two types of damage:
Catastrophic failure - destroyed beyond use
Upset failure - shorten the life of a component
Safety Procedures (4 of 4)
Before touching a component, ground yourself by:
Wearing an ESD strap around your wrist that clips onto the
chassis or computer case
Touching the case before touching any component inside the case
Storing a component inside an antistatic bag
addition to protecting against ESD, always shut down and unplug a
computer before working inside it
Troubleshooting Network Problems
Troubleshooting steps used by most expert networking
troubleshooters:
Identify problem
Gather information
Identify symptoms
Question users
Determine if anything has changed
Establish theory of probable cause
Question the obvious
9
Network+ Guide to Networks, 6th Edition
Troubleshooting Network Problems
Troubleshooting steps
Test theory to determine cause
theory confirmed, determine next steps
theory not confirmed, establish new theory or escalate
Establish action plan
Implement solution or escalate the problem
Verify full functionality
Implement preventative measures if applicable
Document findings, actions, outcomes
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Network+ Guide to Networks, 6th Edition
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Network+ Guide to Networks, 6th Edition
3-0 Week 3 Overview
Topics
Network infrastructure
Types of cables
Ethernet standards
Binary calculation
Learning Objectives
Describe the roles of various network and cabling equipment in
commercial buildings and work areas
Identify types of cables
Describe the Ethernet protocol
Understand how to convert binary
3-1 Infrastructure
Components of Structured Cabling
ANSI/TIA-568 Commercial Building Wiring Standard
Also known as structured cabling
The wiring standard describes the best way to install networking
media to maximise performance and minimise upkeep
The principles apply no matter what type of media, transmission
technology, or networking speeds are involved
Structured cabling is based on a hierarchical design and assumes a
network is based on the star topology
From the Demarc to a Workstation (1 of 11)
From the Demarc to a Workstation (2 of 11)
Entrance Facility in Building A:
(entrance facility) – location where the incoming network (such
as Internet) connects with the school or corporate network
Demarc (demarcation point) – the device that marks where a
telecommunications service provider’s network ends and the
organisation’s network begins
From the Demarc to a Workstation (2 of 11)
Entrance Facility in Building A:
MDF (main distribution frame) – the centralised point of
interconnection for an organisation’s LAN or WAN (also called MC
or main cross connect)
Data room – an enclosed space that hold network equipment (also
called data closet, data centre, equipment room, or
telecommunications room)
Rack – holds various network equipment
Patch panel – a panel of data receptors which can be mounted to
a wall or a rack
patch panel provides a central termination point when many
patch cables converge in a single location
From the Demarc to a Workstation (3 of 11)
From the Demarc to a Workstation (4 of 11)
From the Demarc to a Workstation (5 of 11)
From the Demarc to a Workstation (6 of 11)
Entrance Facility in Building A (continued):
VoIP telephone equipment – VoIP (Voice over IP) is the use of
any network to carry voice signals using TCP/IP protocols
ne or more data rooms you might find the following:
VoIP gateway
VoIP PBX
VoIP endpoints
From the Demarc to a Workstation (6 of 11)
Data Room in Building B:
IDF (intermediate distribution frame) – provides an intermediate
connection between the MDF and end-user equipment on each floor
and in each building
Work Areas in All Three Buildings:
Work area – encompasses workstations, printers, and other
network devices
Wall jacks – the ANSI/TIA standard calls for each wall jack to
contain at least one voice and one data outlet
From the Demarc to a Workstation (7 of 11)
From the Demarc to a Workstation (8 of 11)
From the Demarc to a Workstation (9 of 11)
Rack Systems
Racks come in two-post and four-post varieties (though six-post
racks are also available)
Racks may be wall- or ceiling-mounted, freestanding on the
floor, or bolted to the floor
Consider the following when purchasing racks:
Height – rack height is measured in rack units (RU or U)
with the industry standard being 42U tall
Width – equipment racks come in a standard 19-inch frame (19
inches wide)
Depth – rack depths vary between manufacturers
data centres containing multiple rows of racks, a hot aisle/cold
aisle layout pulls cool air from vents in the floor or from
low-lying wall vents into rows of racks (see Figure 2-14)
From the Demarc to a Workstation (10 of 11)
From the Demarc to a Workstation (11 of 11)
3-2 Cabling
Cabling (1 of 5)
Types of Cables
Patch cable – a relatively short length of cabling with connectors
at both ends
Horizontal cabling – connects workstations to the closest data
room and to switches housed in the room
Backbone cabling – consists of cables or wireless links that
provide interconnection between the entrance facility and MDF and
between MDF and IDFs
Many network problems are the result of poor cable installations
Pay close attention to the quality of cable connections and
cable management
Cabling (2 of 5)
Cabling (3 of 5)
Cabling (4 of 5)
Cable Management
Termination – when terminating twisted-pair cabling, don’t leave
more than 1 inch of exposed cable before a termination
Bend radius – do not exceed the cable’s prescribed bend radius,
which is the radius of the maximum arc into which you can loop a
cable without impairing data transmission
Continuity – use a cable tester to verify that each cable segment
transmits data reliably
Loosely cinch cables
Cabling (4 of 5)
Cable Management
Cable coverings and conduits – avoid laying cables across a floor
and use cord covers if they must be exposed
EMI sources – install cable at least 3 feet away from fluorescent
lights or other sources of EMI (electromagnetic interference)
Plenum cabling – if running cable in the plenum (the area above
the ceiling tile or below subflooring), make sure the cable sheath
is plenum-rated
Cabling (5 of 5)
Cable Management (continued)
Grounding - pay attention to grounding requirements
Slack in cable runs
Cable trays - use cable management devices such as cable trays,
braided sleeving, and furniture grommets
Patch panels - use patch panels to organise and connect lines
Company standards and inventory
Documentation
Keep your cable plant documentation accessible
Label every data jack or port, patch panel and connector
Use color-coded cables for different purposes
Update your documentation as you make changes to the network
3-3 Ethernet
Ethernet (1 of 2)
Ethernet is the most important data link layer standard
capable of running on a variety of network media
Ethernet offers excellent throughput at a reasonable cost
the most popular network technology used on modern LANs
Ethernet II is the current standard
Ethernet adds both a header and a trailer to the payload
This creates a frame around the payload
The header and FCS make up the 18-byte “frame” around the data
The data portion of an Ethernet frame may contain from 46 to 1500
bytes
MTU (maximum transmission unit) is the largest size that routers in a
message’s path will allow at the Network Layer
Ethernet (2 of 2)
Ethernet and the OSI Model
Ethernet operates in two areas of the OSI model:
the lower half of the data link layer, known as the MAC sub layer
and the physical layer
Data link layer – Two Sub-layers
Logical link Control (LLC) : (IEEE 802.2)
The Logical Link Control (LLC) sublayer remains relatively
independent of the physical equipment
Provides an interface between the MAC layer and the Network layer
independent of the hardware
Media Access Control (MAC): (part of IEEE 802.3)
The MAC sub-layer is concerned with the physical components that
will be used to communicate the information
Which computer can access the network when multiple computers are
trying to access it simultaneously
Physical addressing (MAC addresses) and access control methods.
Ethernet Frames
Field name
Length
Description
Preamble and SFD
8 bytes
Signals to the receiving node that bytes following this preamble are the
actual frame. Not included when calculating a frame’s total size.
Header
Destination address
6 bytes
Provides the MAC address of the recipient of the data frame.
Source address
6 bytes
Provides the MAC address of the network node that originally sent the
data.
Type field
2 bytes
Specifies the upper-layer protocol carried in the frame. E.g. an IP packet
has 0x0800 in the Type field.
Data
to 1500 bytes
the data is not at least 46 bytes, padding is added to make a minimum of
46 bytes.
Trailer FCS (frame check sequence)
4 bytes
The FCS trailer ensures that the data at the destination exactly matches
the data issued from the source using the CRC (cyclic redundancy check)
algorithm.
Ethernet Frames
8 bytes
Preamble and SFD
6 bytes
Header
bytes
bytes
46-1500 bytes
Data
4 bytes
Trailer
Types of Ethernet
Mbps Ethernet
Mbps Fast Ethernet
Gigabit Ethernet
Gigabit Ethernet
10BASE5, 10BASE2, and 10BASE-T Ethernet are now considered Legacy
Ethernet
IEEE Ethernet Standards
IEEE 802 Committee Standards:
1 - Standards introduction
2 - Logical Link Control (LLC)
3 - Ethernet
4 - Token Bus - 75 ohm CATV coax or Fibre
5 - Token Ring
6 - MAN (Metropolitan Area Network) - similar to FDDI
7 - Broadband
8 - Fibre Optics
9 - Integrated Voice and Data
10 - LAN Security
11 - Wireless
12 - 100 VG AnyLAN
15 - Bluetooth
16 - WiMax
Ethernet
Ethernet performs three functions:
Transmitting and receiving data frames
Uses CSMA/CD (non-deterministic)
Carrier Sense Multiple Access / Collision Detection
Decoding data frames and checking them for valid MAC addresses
before passing them to the upper layers of the OSI model
Detecting errors within data frames or on the network
Note that Ethernet performs error detection but NOT error
correction
Any frame with an incorrect checksum is an error
Also, any frame under 64 bytes in length is an error
Ethernet
Ethernet was originally designed to work on networks with a shared
medium
physical bus topology
star topology created with a hub
multiple nodes attempt to communicate at the same time, the signals
will interfere
called a collision
CSMA/CD is used for controlling access to the shared medium
CSMA/CD
3-4 Binary
Base 10 Numbers
Base 10 numbers
Base 10 numbers use place value, for example in a four digit number, the
first digit is the thousands place, the second the hundreds, the third the
tens, and fourth the ones.
Place value is determined by exponents. The rightmost place is 100 = 1,
then, going left, 101 = 10, 102 = 100, and so on.
Base 10 uses ten symbols: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9.
Binary Number System
Binary numbers are Base 2. Powers of two are used for place values. So the
rightmost place value is 20 = 1, then going left 21 = 2, 22 = 4, and so
on.
Bits and Bytes
Units
Definition
Bytes (approx.)
Bits (approx.)
Examples
Bit (b)
Binary digit, a 1 or 0
bit
off, open/closed, +5 V or 0 V
Byte (B)
8 bits
1 byte
8 bits
A single character (e.g. “X”) in ASCII code
Kilobyte (KB)
1 kilobyte
= 1024 bytes
bytes
bits
Typical email = 2 KB
10-page doc = 10 KB
Megabyte (MB)
1 megabyte
= 1024 kilobytes
= 1,048,576 bytes
million bytes
million bits
Floppy disk = 1.44 MB
Typical CPU cache = 4 MB
Gigabyte (GB)
1 gigabyte
= 1024 megabytes
= 1,073,741,824 B
billion bytes
billion bits
Typical RAM = 8 GB
Terabyte (TB)
1 terabyte
= 1024 gigabytes
trillion bytes
trillion bits
Amount of data theoretically transmittable in optical fibre in one second.
Some sources will define these units as powers of 1000. So kilobyte = 1000
bytes etc., and will use kibibyte (KiB), mebibyte (MiB), gibibyte (GiB),
and tebibyte (TiB) for definition based on 1024.
Converting Binary to Decimal
= 256
= 128
= 64
= 32
= 16
= 8
= 4
= 2
= 1
bit
1
0
1
1
1
0
1
1
exponent
7
6
5
4
3
2
1
0
value
128
64
32
16
8
4
2
1
128
32
16
8
2
1
187
bit
exponent
7
6
5
4
3
2
1
0
value
128
64
32
16
8
4
2
1
POGIL - Converting Binary to Decimal andDecimal to Binary
Convert 10011101 into decimal
bit
exponent
7
6
5
4
3
2
1
0
value
128
64
32
16
8
4
2
1
POGIL - Converting Binary to Decimal andDecimal to Binary
Convert 10011101 into decimal
What if we had more than 8 bits?
bit
1
0
0
1
1
1
0
1
exponent
7
6
5
4
3
2
1
0
value
128
64
32
16
8
4
2
1
128
16
8
4
1
157
Converting Decimal to Binary
= 256
= 128
= 64
= 32
= 16
= 8
= 4
= 2
= 1
Subtraction method
Example: convert 171 into binary
fits into 171. Write down 1. 171 - 128 leaves 43.1
does not fit into 43. Write down 0.0
fits into 43. Write down 1. 43 - 32 leaves 11.1
does not fit into 11. Write down 0.0
fits into 11. Write down 1. 11 - 8 leaves 3.1
does not fit into 3. Write down 0.0
fits into 3. Write down 1. 3 - 2 leaves 1.1
1. Write down 1. 1 - 1 leaves 0. Done.1
171 = 10101011 in binary.
Converting Decimal to Binary
Remainder method.
Divisor –
Base
Dividend -
Decimal
Remainder –
Binary
Quotient
2
154
154 / 2 = 77 (0 remainder)
77
0
77 / 2 = 38 (1 remainder)
38
1
38 / 2 = 19 (0 remainder)
19
0
19/2 = 9 (1 remainder)
9
1
9 / 2 = 4 (1 remainder)
4
1
4 / 2 = 2 (0 remainder)
2
0
2 / 2 = 0 (0 remainder)
1
0
1 / 2 = 0 (1 remainder)
0
1
10011010
Converting Decimal to Binary
Checking your answer
Make sure you have the correct number of bits
Convert back to decimal to check if you converted correctly
Collision domains are segments of a network where collisions can
potentially occur
Layer 1 devices extend collision domains
Layer 2 devices break up collision domains
3
Broadcast Domains
Nodes on the same LAN exchange data by sending frames
Each frame contains a source and destination MAC address to define the
sender and receiver
Broadcast frames are received by all devices
Layer 1 and 2 devices extend broadcast domains
Layer 3 devices break up broadcast domains
Switches
Switches examine the MAC addresses of frames to determine forwarding
decisions
Unlike hubs, which simply forward all frames out of ports
Switches only send frames out of the port which is connected to the
destination
Hence they break up collision domains
Switches send broadcast frames out of all ports aside from the port
the frame came in
Hence they extend broadcast domains
5
Switches – Bridging Tables
Switches associate interfaces (ports) to MAC addresses in a bridging
table
The bridging table is empty when a switch is first connected
When a frame is received on a given interface, the switch associates
the source MAC address with that interface
a switch sees an unknown destination MAC address, it forwards the
frame on all ports aside from the source port (“flooding”)
6
Switches – Bridging Tables
Switches – Forwarding Decisions
Store-and-Forward
The switch waits until it has received the entire frame and can
verify that it’s valid before forwarding
Slow, but error free
Cut through
The switch begins forwarding the frame as soon as it sees the
destination MAC address
Fast, but errors are passed on
Fragment free
The switch waits until it receives the whole frame header before
forwarding
Slower than cut through, but catches some errors
Collisions in Collision Domain
your Internet router has hub ports instead of switched ports this is
why it slows down when you connect a few extra computers
Collision Domain Segmentation
Layer 1 Devices Extend Collision Domains
Limiting the Collision Domains
Limiting the Collision Domains With a bridge
Broadcasts in a Bridged Environment
Routers
Routers are a layer 3 (Network layer) device
Routers connect networks
Routers building routing tables to all known destination networks by
exchanging their routing tables with adjacent routers.
Routers select the best path for incoming data packets to reach their
destination networks
Routing
Broadcast Domain Segmentation
Welcome to Week 4
Topics
address
DNS
Addressing issues
Learning Objectives
Work with MAC addresses
Configure TCP/IP settings on a computer, including IP address, subnet
mask, default gateway, and DNS servers
Identify the ports of several common network protocols
Describe domain names and the name resolution process
4-1 IP Address
Addressing Overview
There are four addressing methods:
Data link layer MAC (Media Access Control) address is 48 bits,
written as six hex numbers separated by colons
also called a physical address
MAC addresses are embedded on every NIC in the world
Network layer IP (Internet Address) address can be used to find
any computer in the world
IPv4 addresses have 32 bits and are written as four decimal
numbers called octets
IPv6 addresses have 128 bits and are written as eight blocks
of hexadecimal number
Transport layer port numbers are used to find applications
Application layer FQDNs, computer names, and host names
Fully qualified domain name (FQDN) – a unique character-based
name
MAC Addresses (1 of 2)
Traditional MAC addresses contain two parts
The first 24 bits are known as the OUI (Organizationally Unique
Identifier) or manufacturer-ID
This part is assigned by the IEEE
The last 24 bits make up the extension identifier or device ID
Manufacturer’s assign each NIC a unique device ID
Switches use MAC addresses to identify devices on the local area
network
MAC Addresses (2 of 2)
IP Addresses
Static IP addresses are assigned manually by the network administrator
Dynamic IP addresses are automatically assigned by a DHCP server
You’ll learn more about DHCP later in the chapter
There are two types of IP addresses:
IPv4 is a 32-bit address
IPv6 is a 128-bit address
IPv4 Addresses (1 of 4)
32-bit IPv4 address is organized into four groups of 8 bits each
(known as octets)
Each of the four octets can be any number from 0 to 255
Some IP addresses are reserved
Example of an IPv4 address: 72.56.105.12
Classful addressing
The dividing line between the network and host portions is
determined by the numerical range the IP address falls in
Classful IPv4 addresses are divided into five classes:
Class A, Class B, Class C, Class D, and Class E
IPv4 Addresses (2 of 4)
Class A, B, and C licensed IP addresses are available for use on the
Internet
These are called public IP addresses
company can use private IP addresses on its private networks
The IANA recommends the following IP addresses be used for private
networks:
0.0 through 10.255.255.255
0.0 through 172.31.255.255
0.0 through 192.168.255.255
IPv4 Addresses (2 of 4)
Classless addressing allows the dividing line between network and host
portions to fall anywhere along the string of binary bits in an IP
address
CIDR (Classless Interdomain Routing) notation takes the network ID or
a host’s IP address and follows it with a forward slash (/) followed
by the number of bits that are used for the network ID
IPv4 Addresses (3 of 4)
Network Address Translation (NAT) is a technique designed to conserve
public IP addresses needed by a network
Address translation is a process where a gateway device substitutes
the private IP addresses with its own public address
When these computers need access to other networks or Internet
Port Address Translation (PAT) is the process of assigning a TCP port
number to each ongoing session between a local host and Internet host
IPv4 Addresses (3 of 4)
Two variations of NAT to be aware of:
SNAT (Source Network Address Translation) - the gateway assigns
the same public IP address to a host each time it makes a request
to access the Internet
DNAT (Dynamic Network Address Translation) - the gateway has a
pool of public address that it is free to assign to a local host
when it makes a request to access the Internet
IPv4 Addresses (4 of 4)
IPv6 Addresses (1 of 2)
IPv6 address has 128 bits written as eight blocks of hexadecimal
numbers separated by colons
0000:0B80:0000:0000:00D3:9C5A:00CC
Each block is 16 bits
Leading zeros in a four-character hex block can be eliminated
blocks contain all zeroes, they can be written as double colons
(::), only one set of double colons is used in an IP address
Therefore, above example can be written two ways:
:B80:0000:0000:D3:9C5A:CC
B80::D3:9C5A:CC (this is the preferred method because it
contains the fewest zeroes)
IPv6 Addresses (2 of 2)
IPv6 terminology:
link (sometimes called local link) is any LAN bounded by routers
Neighbours are two or more nodes on the same link
Dual stacked is when a network is configured to use both IPv4 and
IPv6
Tunnelling is a method used by IPv6 to transport IPv6 packets
through or over an IPv4 network
Interface ID is the last 64 bits or four blocks of an IPv6 address
that identify the interface
Types of IPv6 Addresses (1 of 4)
Unicast address - specifies a single node on a network
Global address can be routed on the Internet
Link local address can be used for communicating with nodes in the
same link
Loopback address can be used to test that an interface and
supporting protocol stack are functioning properly
Multicast address – delivers packets to all nodes on a network
Anycast address - can identify multiple destinations, with packets
delivered to the closest destination
Types of IPv6 Addresses (2 of 4)
Types of IPv6 Addresses (3 of 4)
Types of IPv6 Addresses (4 of 4)
IPv6 autoconfiguration
IPv6 addressing is designed so that a computer can autoconfigure
its own link local IP address
This process is called SLAAC (stateless address autoconfiguration)
Step 1 - The computer creates its IPv6 address
uses FE80::/64 as the first 64 bits (called prefix)
The last 64 bits are generated from the network adapter’s MAC
address
Step 2 - The computer checks to make sure its IP address is unique on
the network
Step 3 - The computer asks if a router on the network can provide
configuration information
This message is called an RS (router solicitation) message
4-2 The Domain Name System (DNS)
Ports and Sockets (1 of 2)
port is a number assigned to a process that can receive data
Port numbers ensure data is transmitted to the correct process
among multiple processes running on a single device
socket consists of host’s IP address and the port number of an
application running on the host
colon separates the two values
Example - 10.43.3.87:23
Port numbers are divided into three types:
Well-known ports - 0 to 1023
Registered ports - 1024 to 49151
Dynamic and private ports - 49152 to 65535
Ports and Sockets (2 of 2)
Domain Names and DNS (1 of 2)
Character-based names are easier to remember than numeric IP addresses
URL (uniform resource locator) is an addressing scheme that identifies
where to find a particular resource on a network
Last part of an FQDN is called the top-level domain (TLD)
Domain names must be registered with an Internet naming authority that
works on behalf of ICANN
ICANN restricts what type of hosts can be associated with .arpa,
.mil, .int, .edu, and .gov
Name resolution is the process of discovering the IP address of a host
when you know the FQDN
Domain Names and DNS (2 of 2)
DNS is an Application layer client-server system of computers and
databases made up of these elements:
Namespace - the entire collection of computer names and their
associated IP addresses stored in databases on DNS name servers
around the globe
Name servers - hold databases, which are organised in a
hierarchical structure
Resolvers - a DNS client that requests information from DNS name
servers
Namespace Databases
Each organisation that provides host services is responsible for
providing and maintaining its own DNS authoritative servers for public
access
authoritative name server is the authority on computer names and
their IP addresses for computers in their domains
The domains that the organisation is responsible for managing are
called a DNS zone
Name Servers (1 of 4)
Four common types of DNS servers:
Primary DNS server – the authoritative name server for the
organisation
Holds the authoritative DNS database for the organisation’s
zones
Secondary DNS server – backup authoritative name server for the
organisation
Caching DNS server – accesses the public DNS data and caches the
DNS information it collects
Forwarding DNS server – receives queries from local clients but
doesn’t work to resolve the queries
Name Servers (1 of 4)
Any of these DNS server types can co-exist on the same machine
DNS name servers are organised in a hierarchical structure
the root level, 13 clusters of root DNS servers hold information used
to locate top-level domain (TLD) servers
Name Servers (2 of 4)
Name Servers (3 of 4)
Name Servers (4 of 4)
Ways the resolution process can get more complex:
caching server typically is not the same machine as the
authoritative server
The caching server exists only to resolve names for its own
local clients
Name servers within a company might not have access to root
servers
TLD name server might be aware of an intermediate name server
rather than the authoritative name server
Name Servers (4 of 4)
Two types of DNS requests:
Recursive lookup – a query that demands a resolution or the answer
“It can’t be found”
Iterative lookup – a query where the local server issues queries
to other servers
Other servers only provide information if they have it
not demand a resolution
Resource Records in a DNS Database
Several types of records, called resource records are kept in a DNS
database:
SOA (start of authority) record – gives information about the zone
(address) record – stores the name-to-address mapping for a host
AAAA (address) record – holds the name-to-address mapping, the IP
address is an IPv6 type IP address
CNAME (canonical Name) record – holds alternative names for a host
Resource Records in a DNS Database
Several types of records, called resource records are kept in a DNS
database:
PTR (pointer) record – used for reverse lookups
(name Server) record – indicates the authoritative name server for
a domain
(mail exchanger) record – identifies a mail server and is used for
email traffic
SRV (service) record – identifies the hostname and port of a
computer that hosts a specific network services besides email
TXT (text) record – holds any type of free-form text
DNS Server Software
BIND (Berkeley Internet Name Domain) is the most popular DNS server
software
Open source - the term for software whose code is publicly
available for use and modification
Microsoft DNS Server is a built-in DNS service in the Windows Server
OS
Windows Server is capable of split-brain or split-horizon deployment,
which is used to handle internal clients and external clients
4-3 Addressing issues
Troubleshooting Address Problems
Troubleshooting Tools (1 of 8)
Command-line tools are a great resource to troubleshoot network
problems
ping (Packet Internet Groper) utility is used to verify that TCP/IP
is:
Installed
Bound to the NIC
Configured correctly
Communicating with the network
The ping utility sends out a signal called an echo request to another
device (request for a response)
The other computer responds in the form of an echo reply
ICMP (Internet Control Message Protocol) is the protocol used by the
echo request/reply to carry error messages and information about the
network
Troubleshooting Tools (2 of 8)
IPv6 networks use a version of ICMP called ICMPv6
ping6 – on Linux computers running IPv6, use ping6 to verify
whether an IPv6 host is available
ping -6 – on Windows computers, use ping with the -6 switch to
verify connectivity on IPv6 networks
For the ping6 and ping -6 commands to work over the Internet, you must
have access to the IPv6 Internet
Troubleshooting Tools (3 of 8)
The ipconfig command shows current TCP/IP addressing and domain name
information on a Windows computer
Use ipconfig/all to see a more complete summary of TCP/IP
addressing information
Troubleshooting Tools (4 of 8)
Troubleshooting Tools (5 of 8)
Use the ip utility to view and manage TCP/IP settings
The ip utility is only available on UNIX and Linux systems
Any ip commands that change the state of a link require elevated
privileges
This is accomplished by logging in as the root user or by
temporarily elevating the current user's privileges with the sudo
(superuser do) command
ifconfig is a similar utility used to view and manage TCP/IP settings
your Linux or UNIX system provides a GUI
Open a shell prompt, then type ifconfig
Troubleshooting Tools (6 of 8)
Troubleshooting Tools (7 of 8)
The nslookup (name space lookup) utility allows you to query the DNS
database from any computer on a network
find the host name of a device by specifying its IP address, or
vice versa
useful for verifying a host is configured correctly or for
troubleshooting DNS resolution problems
Reverse DNS lookup - to find the host name of a device whose IP
address you know
nslookup 69.23.208.74
Troubleshooting Tools (7 of 8)
The nslookup utility is available in two modes:
Interactive - to test multiple DNS servers at one time
Noninteractive - test a single DNS server
You can change DNS servers from within interactive mode with the
server subcommand and specifying the IP address of the new DNS server
exit nslookup’s interactive mode, enter exit
Troubleshooting Tools (8 of 8)
The dig (domain information groper) utility is available on Linux and
macOS
Provides more detailed information than nslookup and uses more
reliable sources of information to output its results
Use dig to query DNS nameservers for information about host addresses
and other DNS records
IP scanner can be used to gather information about all devices
connected to a network
Common Network Issues (1 of 2)
Incorrect time
Check a domain computer’s time source from a Command Prompt window
by entering w32tm /query /source
DHCP Issues
you are getting DHCP errors or if multiple clients are having
trouble connecting to the network, try the following:
Check the settings on your DHCP server
Make sure the DHCP scope is large enough to account for the
number of clients the network must support
Consider implementing a shorter lease time on larger networks
Common Network Issues (2 of 2)
Network Connection Configuration Issues
Common configuration errors:
Incorrect IP address
Duplicate IP address
Incorrect subnet mask
Incorrect gateway
Incorrect DNS or DNS issues
When a computer is struggling to establish a network connection
Check its TCP/IP configuration settings
the computer is not obtaining an IP address and related
information from a DHCP server
Static settings might be using the wrong information